This invention relates to an improved method for producing polybutene polymers of molecular weights of from 900 to 5000 and polybutene-1 polymers of molecular weights of from 400 to 1500. Polybutene polymers are defined as liquid polymers of which the monomer is predominantly isobutylene. Polybutene-1 polymers are defined as liquid polymers of which the monomers are isobutylene, butene-1 and cis-2-butene. Trans-2-butene is not defined as a monomer of polybutene-1 although trans-2-butene will react in small amounts as a monomer for polybutene-1 under conditions of high temperature (approximately 65.degree. F.).
Polymers of isobutylene and normal butylenes are known, as are methods of preparing these polymers. It has heretofore been supposed that an advantageous method of making such polymers was to use isobutylene which had been purified by fractionation or chemical means. The object of the purification was to remove substantially all or most of the compounds present which acted to "poison" the polymerization of the isobutylene. Olefins other than isobutylene, of more than two carbon atoms, including butene-2, both cis- and trans-butene-1 were considered as "poisons," as well as organic sulfur containing-compounds, alkyl halides, halogen acids, hydrocarbons of high molecular weight, and in general all sulfur, nitrogen and oxygen compounds which could form stable complexes with Friedel-Crafts catalysts. Another method was to polymerize the isobutylene without prior purification; unreacted hydrocarbons were stripped from the product solution, thus avoiding the need to fractionate or purify by chemical means.
These procedures are taught in U.S. Pat. Nos. 2,296,399; 2,384,916; 2,637,720; 2,657,246; 2,775,577; 2,856,394; 3,501,551; and 3,705,884, which are incorporated herein by reference.
However, fractionation to remove the poisons of cis-2-butene, trans-2-butene and butene-1 has been found to remove substantial amounts of isobutylene from the fractionated stream, thus reducing yield of the isobutylene polymer obtainable from the original feed streams. Fractionation of cis-2-butene and trans-2-butene with or without concurrent fractionation to remove butene-1 results in determinable amounts of isobutylene being returned to the refinery as bottoms of little value. For example, it has been found that in a typical fractionation (using a column of 58 trays) of a feed stream to remove 52.4% cis-2-butene, and 45.0% trans-2-butene, approximately 3.6 times more isobutylene is removed than in fractionating to remove 48.0% cis-2-butene and 40.1% trans-2-butene.
Accordingly, it is an object of the present invention to provide an improved method of preparing isobutylene polymers having molecular weights of from 900 to 5000 from a butene-isobutylene stream suitable for alkylating mononuclear aromatic hydrocarbons. It is another object of this invention to provide an improved method of preparing isobutylene, butene-1, cis-2-butene polymers, known as polybutene-1, polymers, having molecular weights of from 400 to 1500, which polymers are suitable for conversion to sulfonates for motor oil additives. It is another object of this invention to provide an increased supply of butylene polymers from butene-isobutylene feedstocks which are in short supply. Other objects and advantages of the instant invention will become apparent as the detailed description proceeds.